I have to synchronize a folder after each appointment creation. So, user can't have to wait 30 seconds each time !

Please, could someone tell me whether it's normal that an appointments folder make 30seconds to synchronize ?
How can I reduce this duration ?

Maybe I did not the right choice by handling the folder like this, rather than using a mountpoint that doesn't need synchronization after appointment creation.
But with a mountpoint, I can't tell that calB's appointments have to be shown as "busy" for B user (in my precedent example).

Maybe is there a better way ? My need is that user B can see appointments as busy, but can't modify them directly : they are handled (creation, modification,...) by the business application, through SOAP call.